Former US presidential contender John McCain, who spent five years as a prisoner of war in the infamous "Hanoi Hilton," has returned to Vietnam as a welcome, but controversial guest.

Mr McCain visited the city lake into which he parachuted after his F4-Skyhawk bomber was shot down in 1967 at the height of the war, and is scheduled to visit his former prison on Wednesday

My job here is to commemorate the beginning and continuation of a new relationship

John McCain

Despite his five-year stint as a POW, Mr McCain has become a strong advocate of normalising ties between Vietnam and the United States.

"My job here is to commemorate the beginning and continuation of a new relationship between the United States and Vietnam," he said.

Birth defects

The visit coincides with celebrations underway in Vietnam to mark the 25th anniversary of the war's end on 30 April 1975.

Vietnamese officials told Mr McCain that the country was still suffering from the legacy of the war, especially the use of the defoliant Agent Orange.

Scientists say thousands of people may have suffered cancer and birth defects caused by the deadly chemical dioxin, contained in Agent Orange.

During a brief airport news conference Mr McCain was asked if he felt any lingering bitterness from the war.

"I put the Vietnam War behind me a long time ago," he said. "I harbor no anger, no rancor."

MIA veterans commemorated

Following his arrival, Mr McCain attended a sombre ceremony at Hanoi's Noi Bai airport in which remains believed to be those of six US servicemen missing in action were put aboard a plane heading to Hickam Air Force Base in Hawaii for forensic analysis.

Veterans return home

Nearly 50 US civilians and military personnel were present for the ceremony, held in silence except for a few clipped military commands.

The remains were recovered this year as part of the ongoing American effort to account for the nearly 2,000 servicemen still missing.

Hanoi says more than 300,000 Vietnamese are still missing from the war.

An awkward visit

McCain's five-day visit may have some awkward moments.

John McCain's words have hurt the Vietnamese and Asian peoples

Vietnam Foreign Ministry spokesman Phan Thuy Thanh

During his unsuccessful bid for the presidency earlier this year, Mr McCain spoke of being tortured by his Vietnamese guards, that he and his fellow prisoners referred to in the derogatory term "gooks."

Vietnam has denied that prisoners were tortured.

Some Asian-American groups criticised Mr McCain's language and urged him to apologise, but he declined.

"John McCain's words and statements, which lack goodwill, have hurt the Vietnamese and Asian peoples," Vietnam Foreign Ministry spokesman Phan Thuy Thanh said in February at the height of the controversy.

A hellish stay in Hanoi

Mr McCain's plane was downed on 26 October 1967, and he was fished out of Hanoi's Truc Bach lake by a Vietnamese civilian.

He made a 15-minute visit there on Tuesday, walking along the shore to a memorial of the incident.

"Everything happened very quickly," he said. "I broke both my arms and a leg, and I was dragged ashore and I was beaten."

Mr McCain was held until March 1973 at Hoa Lo Prison, which the POWs nicknamed the "Hanoi Hilton."

He said he endured three years of solitary confinement for what his captors called a "bad attitude".

He twice tried to hang himself, using his shirt as a noose, but was caught both times by the guards, and subsequently beaten.

Most of the prison was torn down in 1993, but one wing was preserved and opened as a museum three years ago.

One cell is devoted to the 300 American prisoners detained there and includes a photo of the young McCain with several days' worth of stubble on his face.